Method for reactivation of platinum group metal catalyst with aqueous alkaline and/or reducing solutions

ABSTRACT

A method for reactivation of a platinum group metal catalyst which comprises treating the platinum group metal catalyst lowered in catalytic activity as the result of having been used for the catalytic reaction of hydrocarbons optionally containing an oxygen atom with at least one agent selected from an inorganic alkaline substance and a reducing substance in an aqueous medium.

The present invention relates to a method for reactivation of a platinum group metal catalyst. More particularly, it relates to a method for reactivation of a platinum group metal catalyst lowered in catalytic activity as the result of having been used for the catalytic reaction of hydrocarbons optionally containing an oxygen atom.

Conventional catalysts of this type which have been used in the catalytic reaction of hydrocarbons optionally containing an oxygen atom, such as in the steam-reforming of hydrocarbons, hydro-cracking of hydrocarbons, partial oxidation of hydrocarbons and steam-reforming of alkanols, include base metal (e.g. Fe, Ni, Co) catalysts and noble metal (e.g. Pt, Pd, Ru) catalysts. In comparison with the base metal catalysts (particularly nickel catalysts), the noble metal catalysts (particularly platinum group metal catalysts) possess certain advantages as, for instance, resistance to the deposition of carbonaceous materials thereon and maintenance of high catalytic activity with use in small amounts. However, due to the expensiveness of the noble metal catalysts, the practical considerations have been concentrated in the use of the base metal catalysts. In order to overcome this shortcoming, attempts have been made to reactivate noble metal catalysts lowered in the catalytic activity so as to enable their reuse. Typical conventional procedures for such reactivation include treatment with hydrogen, steam or oxygen, and in fact, such procedures are quite effective in the elimination of certain poisonous materials in addition to the carbonaceous materials deposited on the catalysts. However, the recovery of the catalytic activity provided by these procedures is frequently not satisfactory.

In general, catalytic reactions of hydrocarbons optionally containing an oxygen atom in the presence of a platinum group metal catalyst result in deposition of various materials such as carbonaceous materials and sulfurous materials on the catalyst particles. In addition, these catalytic reactions often result in a sintering of the catalyst particles causing their mutual cohesion, whereby the particle size of the catalyst enlarged and the dispersibility of the catalyst consequently lowered. Further, the physical and chemical constitutions and behaviors of the catalysts may be gradually changed during the catalytic reactions. Due to these and other factors which are still unclear, the catalytic activity of the catalyst is lowered during the course of the catalytic reaction. In order for recovery of the catalytic activity to reach a practically satisfactory level, it is necessary to substantially reduce or eliminate these adverse factors.

As the result of extensive study, it has now been found that treatment of platinum group metal catalysts lowered in catalytic activity by contact with at least one agent selected from an inorganic alkaline substance and a reducing substance in an aqueous medium provides an effective recovery of the catalytic activity. It has also been found that the combination of treatments with both an inorganic alkaline substance in an aqueous medium and a reducing substance in an aqueous medium is particularly effective for accomplishment of the reactivation. It has further been found that the reactivation effected by the treatment with the inorganic alkaline substance and/or the reducing substance can be more assured by treating the catalyst lowered in catalytic activity with hydrogen, steam or oxygen before or after the treatment with the inorganic alkaline substance and/or the reducing substance.

It may be noted that conventional treatment with hydrogen, steam or oxygen is effective for the removal of carbonaceous materials deposited on the catalyst but not for the elimination of sulfurous materials. On the other hand, treatment with an inorganic alkaline substance or a reducing substance is highly effective for the removal of sulfurous materials though the effect of elimination of carbonaceous materials may be not as high as obtained by conventional treatment with hydrogen, steam or oxygen. Particularly notable is the fact that while the conventional treatment has almost no effect on the recovery of the lowered catalytic activity, treatment with an inorganic alkaline substance or a reducing substance has a surprisingly significant effect.

According to the present invention, the reactivation of a platinum group metal catalyst lowered in the catalytic activity is carried out by treatment of the catalyst with at least one inorganic alkaline substance or at least one reducing substance or both, in an aqueous medium.

The platinum group metal catalyst to be subjected to the treatment in the present invention may be the one which comprises a platinum group metal such as ruthenium, rhodium, palladium, osmium, iridium or platinum as the catalyst component deposited on a carrier material such as alumina, magnesia, zirconia, titania, silica, silica-alumina, silica-magnesia, alumina-magnesia or carbon and lowered in catalytic activity as the result of having been used for the catalytic reaction of hydrocarbons optionally containing an oxygen atom. In addition to the said essential catalyst component, the platinum group metal catalyst may comprise any additive which does not materially afford any unfavorable influence thereon. Examples of the additive include any material known as the so-called "co-catalyst" such as alkali metals, alkaline earth metals, iron, copper, nickel, cobalt, chromium, tungsten, manganese or molybdenum. The term "hydrocarbons optionally containing an oxygen atom" hereinabove used is intended to mean organic compounds consisting of carbon atoms and hydrogen atoms or of carbon atoms, hydrogen atoms and oxygen atoms, and their examples include aliphatic hydrocarbons, aromatic hydrocarbons, naphthenic hydrocarbons, alkanols, alkanones, etc. Examples of the catalytic reaction are steam-reforming of hydrocarbons, hydro-cracking of hydrocarbons, partial oxidation of hydrocarbons, steam-reforming of alkanols, etc.

The inorganic alkaline substance may be an inorganic alkaline compound containing at least one alkali metal or alkaline earth metal. Examples of the alkali metals and the alkaline earth metals are sodium, potassium, calcium, magnesium, barium, strontium, etc. Preferred examples of the inorganic alkaline compounds containing these alkali metals and alkaline earth metals are hydroxides, carbonates, nitrates, sulfates, etc. or mixtures thereof. The concentration of the inorganic alkaline substance in the aqueous medium may be varied depending upon the amount of the catalyst component deposited on the carrier material, the degree of lowered catalytic activity, the temperature and pressure at which the reactivation treatment is carried out and the like. In general, however, the concentration is usually from about 0.001 to 10 N, preferably from about 0.001 to 5 N.

As the reducing substance, there may be employed normally water-soluble or water-dispersible reducing substances such as hydrazine, formaldehyde, sodium borohydride, lithium aluminum hydride, sodium tartrate, potassium tartrate, sodium potassium tartrate, calcium tartrate, sodium hydrogen tartrate, sodium formate, potassium formate, calcium formate, glucose, etc. or mixtures thereof. The concentration of the reducing substance in the aqueous medium depends on the amount of the catalyst component deposited on the carrier material, the degree of lowered catalytic activity, the temperature and pressure employed in the reactivation treatment, etc. Normally it falls in the range of about 0.01% to 10% by weight.

Even when the catalyst lowered in catalytic activity is treated solely with the inorganic alkaline substance or the reducing substance, appreciable elimination of sulfurous materials deposited on the catalyst and considerable recovery of the catalytic activity can be attained by choosing appropriate conditions for the treatment. In general, however, the treatment is preferably carried out in two separate steps, i.e. by treatment with the inorganic alkaline substance and then treatment with the reducing substance, or vice versa. When desired, such a two step treatment may be repeatedly applied until a satisfactory recovery of the catalytic activity is achieved, though a single application of two step treatment is usually sufficient.

The treatment with the inorganic alkaline substance is usually effected at room temperature (i.e. about 5° to 30° C.) or while heating under atmospheric pressure or an elevated pressure. However, it can be widely varied depending on the extent of lowered catalytic activity, the composition of the catalyst, the kind of the inorganic alkaline substance employed, etc. In general, a higher temperature affords a better result, but too high a temperature should be avoided since the carrier material may be unfavorably dissolved. Thus, the temperature is usually from about 5° to 250° C., preferably from about 50° to 200° C. The pressure may be appropriately selected so as to maintain the system for treatment in a liquid state, and such pressures do not usually exceed 50 kg/cm².

Treatment with the reducing substance may be carried out at a temperature from room temperature to the decomposition temperature of the reducing substance under atmospheric pressure or at an elevated pressure. Although the temperature is considerably affected by various factors such as the extent to which the catalytic activity is lowered, the composition of the catalyst and the kind of the reducing substance, the temperature is ordinarily between room temperature and about 250° C., insofar as the reducing substance is not decomposed. The pressure may be appropriately selected so as to keep the system in a liquid state and is normally not higher than 50 kg/cm².

When combined two step treatments with the inorganic alkaline substance and with the reducing substance are effected in this order or vice versa, these may be performed with or without intervention of water-washing and/or drying between them.

The treatment(s) with the inorganic alkaline substance and/or with the reducing substance may be effected until a satisfactory recovery of the catalytic activity is attained. Usually, treatment(s) effected so as to eliminate not less than about 40% of carbonaceous materials and not less than about 70% of sulfurous materials deposited on the catalyst will achieve the satisfactory recovery of the catalytic activity. The contact or treating time employed will vary depending upon many factors such as whether one or two step treatments are used, the degree of recovery of catalytic activity desired, etc. Usually a treating time of several minutes to several tens hours (e.g. 3 minutes to 80 hours) is generally sufficient to achieve the aforementioned satisfactory recovery of catalytic activity. However, as stated above, the deterioration of the catalytic activity is caused not only by deposition of carbonaceous and/or sulfurous materials but also by other unclear factors, and therefore the elimination of the said deposited materials may not always be sufficient for recovery of the catalytic activity. If necessary, therefore, the said treatment(s) with the inorganic alkaline substance and/or with the reducing substance may be carried out in combination with any conventional reactivation treatment. For instance, the treatment of the catalyst with hydrogen, steam or oxygen may be effected prior to, between or subsequent to the treatment(s) with the inorganic alkaline substance and/or with the reducing substance.

Examples of usable gases for the conventional reactivation treatment are hydrogen, oxygen, steam, a mixture of hydrogen and steam, a mixture of oxygen and steam, etc. These gases may be optionally diluted with any other inert gas such as nitrogen, helium or argon. Particularly preferred are (1) hydrogen, (2) a mixture of hydrogen and steam having a hydrogen content of not less than about 30 mol%, (3) a mixture of steam and a gaseous diluent having a steam content of not less than about 30 mol%, (4) a mixture of oxygen and a gaseous diluent having an oxygen content of not less than about 0.5% by volume, (5) a mixture of oxygen, steam and a gaseous diluent having an oxygen content of not less than about 0.5% by volume and a steam content of not less than about 30% by volume, etc.

The conditions for treatment with the said gases depend on the amount of the catalyst component deposited on the carrier material, the deposited amount of poisonous materials (particularly carbonaceous materials), the concentration of the active gases, the kind of other treatment procedures employed, etc. Usually a temperature of about 350° to 750° C. and a pressure of about 1 to 50 atm. (absolute) are adopted. The treatment may be continued until the deposited amount of poisonous materials, particularly carbonaceous materials, is appreciably decreased. When the deposited amount of carbonaceous materials is relatively large, the generation of heat occurs sometimes. In such case, the oxygen content in the treating gases may be decreased or the use of the treating gases containing no oxygen is preferred.

After the finalization of the treatment(s) as explained above, the resulting catalyst may be washed with water and/or dried. Particularly, when the final step is the treatment with the inorganic alkaline substance or the reducing agent in an aqueous medium, water washing and drying are favorable.

As stated above, the thus reactivated catalyst is satisfactorily recovered in catalytic activity. Even when the catalyst is severely poisoned and its catalytic activity is extremely lowered, the repeated application of the above treatment(s) enables the satisfactory recovery of catalytic activity nearly equal to that of a freshly prepared catalyst. Further, when the once reactivated catalyst is lowered again in the catalytic activity, the repeated application of the above treatment(s) will reactivate it. Thus, the present invention is quite advantageous in making it possible to use an expensive platinum group metal catalyst repeatedly.

Practical and presently preferred embodiments of the present invention are illustratively shown in the following Examples wherein part(s) and % are by weight unless otherwise indicated. The amount of the catalyst required for reaction indicates a minimum amount of the catalyst required for showing a catalytic activity for reaction.

EXAMPLE 1

A catalyst comprising 2.0% of ruthenium and 0.1% of chromium oxide deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (hereinafter referred to as "Catalyst A₁ ") (325 ml) was charged into a tubular reactor of 1 inch in diameter, and a gaseous mixture comprising naphtha (content of sulfur, 2 ppm; final boiling point, 168° C.), steam, hydrogen, methane and carbon oxides was fed therein to effect continuously steam-reforming reaction for 1500 hours under the following conditions:

Temperature of reactor: inlet, 450° C., outlet, 524° C.;

Space velocity: 2000 (l/hr);

Ratio of steam/hydrocarbon: 0.9 (number of oxygen atoms per one carbon atom in the feeding gaseous mixture);

Pressure: 13 atm. (absolute)

After 1500 hours, the resultant catalyst (hereinafter referred to as "Catalyst B₁ ") was treated under the conditions as shown in Table 1 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 1.

As seen from Table 1, the reactivation treatment with hydrogen is extremely effective for elimination of carbonaceous materials, but removal of sulfurous materials is insufficient and the dispersibility can be hardly recovered so that recovery of the catalytic activity is scarcely observed (Catalysts C₁ -1 and C₁ -2). In the case of treatment with an inorganic alkaline substance, elimination of sulfurous materials and recovery of the dispersibility as well as recovery of the catalytic activity are good.

                                      Table 1                                      __________________________________________________________________________                       Reactivated                                                  Catalyst    A.sub.1                                                                           B.sub.1                                                                           C.sub.1 -1                                                                         C.sub.1 -2                                                                          D.sub.1 -1                                                                          D.sub.1 -2                                                                          D.sub.1 -3                                                                          D.sub.1 -4                                                                         D.sub.1 -5                                                                         D.sub.1 -6                   __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          -- -- H.sub.2                                                                            O.sub.2 :N.sub.2                                                                    0.375N                                                                              0.375N                                                                              0.375N                                                                              1.0N 5.0N                                                                              0.375N                       tions                                                                               agent (*)        (=21:                                                                               NaOH NaOH NaOH NaOH NaOH                                                                              Na.sub.2 CO.sub.3            of                    79 by                                                    treat-                volume)                                                  ment                                                                           for  Temper-                                                                               -- -- 650 500  50   70   100  100  70 100                          reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              -- -- 6.0 6.0  1.0  1.0  1.0  1.0  1.0                                                                               1.0                               (ata)                                                                          Time (hrs)                                                                            -- -- 12  5    6.0  3.0  1.5  0.75 0.5                                                                               3.0                               Post-treat-                                                                           -- -- --  --   Water washing: 100° C., 2 hrs.                    ment                  Drying: 100° C., 16 hrs.                     Elimina-                                                                            Carbo- -- -- 100 100  41   46   55   54  59  54                           tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             -- -- 33  40   78   84   95   97  100 93                           materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43 20 19  17   28   30   35   37  37  36                            (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         52.5                                                                              -- --  --   85   68   63   63  61  64                           required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________      (*) In case of Catalysts C.sub.1 -1 and C.sub.1 -2, the treatment was          carried out with a space velocity of 2500 (l/hr).                        

    Reactivated                                                                    Catalyst     D.sub.1 -7                                                                            D.sub.1 -8                                                                            D.sub.1 -9                                                                            D.sub.1 -10                                                                           D.sub.1 -11                                                                           D.sub.1 -12                    __________________________________________________________________________     Condi-                                                                               Reactivating                                                                          0.375N 0.375N 0.375N 0.375N 0.375N 0.001N                         tions agent  KOH    Ba(OH).sub.2                                                                          Sr(OH).sub.2                                                                          NaOH   NaOH   NaOH                           of                                                                             treat-                                                                         ment                                                                           for   Temper-                                                                               100    100    100    148    205    100                            reacti-                                                                              ature (° C.)                                                      vation                                                                               Pressure                                                                              1.0    1.0    1.0    5.0    20.0   1.0                                  (ata)                                                                          Time (hrs)                                                                            3.0    3.0    3.0    1.0    0.5    10.0                                 Post-treat-                                                                           Water washing: 100° C., 2 hrs.                                   ment   Drying: 100° C., 16 hrs.                                   Elimina-                                                                             Carbo- 52     50     48     56     58     40                             tion per-                                                                            naceous                                                                  centage                                                                              materials                                                                of                                                                             poisonous                                                                            Sulfurous                                                                             90     87     87     100    100    80                             materials                                                                            materials                                                                (%)                                                                            Specific surface area                                                                       35     33     32     34     37     30                              (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                          64     66     68     63     60     69                             required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 2

A catalyst comprising 0.3% of ruthenium deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (1000 ml) was charged into a tubular reactor of 1 inch in diameter, and naphtha (final boiling point, 108° C.) and hydrogen were fed therein to effect continuously hydro-cracking reaction under the following conditions:

Temperature of reactor at inlet: 265° C.;

Pressure: 46 atm. (absolute);

Ratio of hydrogen/hydrocarbon: 1.20 (by mol)

Mass velocity: 500 kg-mol/m². hr

The conversion of hydrogen at the initial stage was 82%, and the catalytic activity was materially decreased after about 200 hours. The resultant catalyst was heated in a 0.375 N aqueous solution of sodium hydroxide at 100° C. for 3 hours, washed with water at 100° C. for 2 hours and then dried at 100° C. for 16 hours. The thus reactivated catalyst was reused for hydro-cracking under the same conditions as above, whereby a conversion of hydrogen of 80% was observed.

EXAMPLE 3

A catalyst comprising 2.6% of ruthenium and 0.1% of chromium oxide deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (hereinafter referred to as "Catalyst A₂ ") (325 ml) was charged into a tubular reactor of 1 inch in diameter, and a gaseous mixture comprising naphtha (content of sulfur, 2 ppm; final boiling point, 168° C.), steam, hydrogen, methane and carbon oxides was fed therein to effect continuously steam-reforming reaction for 2400 hours under the following conditions:

Temperature of reactor: inlet, 400° C., outlet, 517° C.;

Space velocity: 1500 (l/hr);

Ratio of steam/hydrocarbon: 0.7 (number of oxygen atoms per one carbon atom in the feeding gaseous mixture);

Pressure: 13 atm. (absolute)

After 2400 hours, the resultant catalyst (hereinafter referred to as "Catalyst B₂ ") was treated under the conditions as shown in Table 2 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 2.

As seen from Table 2, the reactivation treatment with hydrogen is extremely effective for elimination of carbonaceous materials, but removal of sulfurous materials is insufficient and the dispersibility can be hardly recovered so that recovery of the catalytic activity is scarcely observed (Catalyst C₂). In the case of treatment with an inorganic alkaline substance at room temperature, elimination of sulfurous materials and recovery of the dispersibility are relatively good when the treating time is long, but the recovery of the catalytic activity is insufficient (Catalysts D₂ -1 and D₂ -2). The treatment with an inorganic alkaline substance under heating is proved to be effective for recovery of the catalytic activity (Catalysts D₂ -3 to D₂ -5). In the treatment with a reducing substance, elimination of sulfurous material is good, but removal of carbonaceous materials is hardly attained. There is a tendency to recovery of the catalytic activity (Catalysts D₂ -6 to D₂ -13).

                                      Table 2                                      __________________________________________________________________________                       Reactivated                                                  Catalyst    A.sub.2                                                                           B.sub.2                                                                           C.sub.2                                                                            D.sub.2 -1                                                                          D.sub.2 -2                                                                          D.sub.2 -3                                                                          D.sub.2 -4                                                                          D.sub.2 -5                                                                          D.sub.2 -6                                                                         D.sub.2 -7                  __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          -- -- H.sub.2                                                                            0.375N                                                                              0.375N                                                                              0.375N                                                                              0.375N                                                                              0.375N                                                                              0.4%                                                                               0.3%                        tions                                                                               agent (*)        NaOH NaOH NaOH NaOH NaOH Hydra-                                                                             Lithium                     of                                             zine                                                                               aluminum                    treat-                                             hydride                     ment                                                                           for  Temper-                                                                               -- -- 650 30   30   50   100  148  20  20                          reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              -- -- 6.0 1.0  1.0  1.0  1.0  5.0  1.0 1.0                              (ata)                                                                          Time (hrs)                                                                            -- -- 12.0                                                                               3.0  10.0 6.0  3.0  1.0  3.0 3.0                              Post-treat-                                                                           -- -- --  Water washing: 100° C., 2 hrs.                                                                   Water washing:                       ment             Drying: 100° C., 16 hrs.                                                                         75° C., 3 hrs.                                                          Drying: 100° C.,                                                        16 hrs.                         Elimina-                                                                            Carbo- -- -- 100 12   41   43   52   56    0   0                          tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             -- -- 31  32   72   78   90   100  68  49                          materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43 17 17  21   27   28   34   35   21  23                           (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         92 -- --  --   --   147  110  106  276 270                         required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________      (*) In case of Catalyst C.sub.2, the treatment was carried out with a          space velocity of 2500 (l/hr).  -                                        

    Reactivated                                                                    Catalyst    D.sub.2 -8                                                                             D.sub.2 -9                                                                             D.sub.2 -10                                                                            D.sub.2 -11                                                                           D.sub.2 -12                                                                           D.sub.2 -13                  __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.7%    2.0%    0.3%    1.0%   1.0%   1.0%                         tions                                                                               agent  Sodium  Sodium  Glucose Hydra- Formal-                                                                               Sodium                       of          tart-   formate         zine   dehyde boro-                        treat-      rate                                  hydride                      ment                                                                           for  Temper-                                                                               20      20      20      60     60     60                           reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0     1.0     1.0     1.0    1.0    1.0                               (ata)                                                                          Time (hrs)                                                                            3.0     3.0     3.0     3.0    3.0    3.0                               Post-treat-                                                                           Water washing: 75° C., 3 hrs.                                    ment   Drying: 100° C., 16 hrs.                                    Elimina-                                                                            Carbo-  0       0       0       0      0      0                           tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             46      53      49      90     67     88                           materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      23      23      23      23     23     23                            (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         272     272     276     266    270    276                          required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 4

The reactivated catalysts as obtained in Example 3 (Catalysts D₂ -1 to D₂ -4 and D₂ -6 to D₂ -12) were each subjected to further treatment for reactivation under the conditions as shown in Table 3. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 3. The results are shown in Table 3.

As seen from Table 3, the catalysts (E₃ -1 to E₃ -20) reactivated in two steps are much more recovered in catalytic activity than the catalysts (D₂ -1 to D₂ -4 and D₂ -6 to D₂ -12) reactivated in one step.

                                      Table 3                                      __________________________________________________________________________     Catalyst    E.sub.3 -1                                                                          E.sub.3 -2                                                                          E.sub.3 -3                                                                          E.sub.3 -4                                                                          E.sub.3 -5                                                                          E.sub.3 -6                                                                          E.sub.3 -7                                                                          E.sub.3 -8                                                                          E.sub.3 -9                                                                          E.sub.3 -10           Catalyst used                                                                              D.sub.2 -1                                                                          D.sub.2 -2                                                                          D.sub.2 -3                                                                          D.sub.2 -3                                                                          D.sub.2 -4                                                                          D.sub.2 -4                                                                          D.sub.2 -6                                                                          D.sub.2 -6                                                                          D.sub.2 -11                                                                         D.sub.2 -12           __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          1.0% 0.4% 0.4% 0.5% 0.4% 0.3% 0.375N                                                                              0.375N                                                                              0.375N                                                                              0.375N                tions                                                                               agent  Hydra-                                                                              Hydra-                                                                              Hydra-                                                                              Formal-                                                                             Hydra-                                                                              Sodium                                                                              NaOH NaOH NaOH NaOH                  of          zine zine zine dehyde                                                                              zine boro-                                     treat-                               hydride                                   ment                                                                           for  Temper-                                                                               60   20   20   20   20   20   50   100  100  80                    reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                        (ata)                                                                          Time (hrs)                                                                            3.0  3.0  3.0  3.0  3.0  3.0  6.0  3.0  3.0  3.0                        Post-treat-                                                                           Water washing: 75° C., 3 hrs.                                                                         Water washing: 100° C.,                                                 2 hrs.                                    ment   Drying: 100° C., 16 hrs.                                                                              Drying: 100° C., 16                                                     hrs.                                 Elimina-                                                                            Carbo- 12   41   43   43   52   52   43   54   53   47                    tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             89   91   93   93   97   95   91   97   95   89                    materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      34   36   36   36   40   40   35   39   41   39                     (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         108  110  102  106  95   98   102  95   93   95                    required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________     Catalyst    E.sub.3 -11                                                                          E.sub.3 -12                                                                          E.sub.3 -13                                                                        E.sub.3 -14                                                                        E.sub.3 -15                                                                          E.sub.3 -16                                                                         E.sub.3 -17                                                                         E.sub.3 -18                                                                        E.sub.3 -19                                                                         E.sub.3 -20           Catalyst used                                                                              D.sub.2 -1                                                                           D.sub.2 -2                                                                           D.sub.2 -3                                                                         D.sub.2 -3                                                                         D.sub.2 -4                                                                           D.sub.2 -4                                                                          D.sub.2 -7                                                                          D.sub.2 -8                                                                         D.sub.2 -9                                                                          D.sub.2 -10           __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.3%  0.3%  0.7%                                                                               2.0%                                                                               0.3%   0.3%                                                                               0.375N                                                                              0.1N                                                                               0.375N                                                                              0.375N                tions                                                                               agent  Lithium                                                                              Lithium                                                                              Sodium                                                                             Sodium                                                                             Lithium                                                                              Glucose                                                                             NaOH NaOH                                                                               NaOH NaOH                  of          aluminum                                                                             aluminum                                                                             tart-                                                                              formate                                                                            aluminum                                       treat-      hydride                                                                              hydride                                                                              rate    hydride                                        ment                                                                           for  Temper-                                                                               20    20    20  20  20    20   50   100 100  80                    reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0   1.0 1.0 1.0   1.0  1.0  1.0 1.0  1.0                        (ata)                                                                          Time (hrs)                                                                            3.0   3.0   3.0 3.0 3.0   3.0  6.0  3.0 1.5  3.0                        Post-treat-                                                                           Water washing: 75° C., 3 hrs.                                                                          Water washing: 100° C.,                                                 2 hrs.                                   ment   Drying: 100° C., 16 hrs.                                                                               Drying: 100° C., 16                                                     hrs.                                Elimina-                                                                            Carbo- 12    41    43  43  52    52   43   44  46   47                    tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             66    86    89  90  95    95   89   88  93   92                    materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      31    36    37  37  41    40   38   37  37   37                     (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         126   106   100 100 94    95   98   100 100  100                   required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 5

The reactivated catalyst obtained in Example 3 (Catalyst D₂ -3) was treated with a 0.4% aqueous solution of hydrazine at 20° C. under 1 atm. (absolute) for 3 hours, washed with water at 75° C. for 3 hours and dried at 100° C. for 16 hours. Then, the resulting catalyst was again subjected to treatment with a 0.375 N aqueous solution of sodium hydroxide at 50° C. under 1 atm. (absolute) for 6 hours and treatment with a 0.4% aqueous solution of hydrazine at 20° C. under 1 atm. (absolute) for 3 hours, followed by washing with water at 75° C. for 3 hours and drying at 100° C. for 16 hours. The thus reactivated catalyst was used for steam-reforming under the same conditions as stated in Example 3. The results are as follows: elimination percentage of poisonous materials: carbonaceous materials, 75%; sulfurous material, 100%. Specific surface area: 42 m² /g-Ru. Amount of catalyst required for reaction: 93 ml.

As seen from the above results, the repeating treatments with an inorganic alkaline substance and with a reducing substance are quite effective for reactivation of the catalyst.

EXAMPLE 6

The reactivated catalyst obtained in Example 3 (Catalyst D₂ -3) was treated with a 0.7% aqueous solution of sodium tartrate at 20° C. under 1 atm. (absolute) for 3 hours, washed with water at 75° C. for 3 hours and dried at 100° C. for 16 hours. Then, the resulting catalyst was again subjected to treatment with a 0.375 N aqueous solution of sodium hydroxide at 50° C. under 1 atm. (absolute) for 6 hours and treatment with a 0.7% aqueous solution of sodium tartrate at 20° C. under 1 atm. (absolute) for 3 hours, followed by washing with water at 75° C. for 3 hours and drying at 100° C. for 16 hours. The thus reactivated catalyst was used for steam-reforming under the same conditions as stated in Example 3. The results are as follows: elimination percentage of poisonous materials: carbonaceous materials, 70%; sulfurous material, 100%. Specific surface area: 42 m² /g-Ru. Amount of catalyst required for reaction: 93 ml.

As seen from the above results, the repeating treatments with an inorganic alkaline substance and with a reducing substance are quite effective for reactivation of the catalyst.

EXAMPLE 7

A catalyst comprising 3.8% of ruthenium deposited on spheroidal particles of alumina of 4 mm in diameter (hereinafter referred to as "Catalyst A₄ ") (325 ml) was charged into a tubular reactor of 1 inch in diameter, and naphtha (content of sulfur, 2 ppm; final boiling point, 220° C.) and steam were fed therein to effect continuously steam-reforming reaction for 750 hours under the following conditions:

Temperature of reactor: inlet, 510° C., outlet, 518° C.;

Space velocity: 2000 (l/hr);

Ratio of steam/hydrocarbon: 1.9 (number of oxygen atoms per one carbon atom in the feeding gaseous materials);

Pressure: 13 atm. (absolute)

After 750 hours, the catalyst (hereinafter referred to as "Catalyst B₄) was treated under the same conditions as shown in Table 4 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 4.

As seen from Table 4, treatment with an inorganic alkaline substance shows recovery of the catalytic activity, and treatment with a reducing substance shows a tendency to recovery of the catalytic activity. However, when the catalyst is severely polluted, an elevated temperature is necessary for satisfactory recovery of the catalytic activity by treatment with an inorganic alkaline substance.

                                      Table 4                                      __________________________________________________________________________                           Reactivated                                              Catalyst    A.sub.4                                                                             B.sub.4                                                                             C.sub.4                                                                             D.sub.4 -1                                                                          D.sub.4 -2                                                                          D.sub.4 -3                                                                          D.sub.4 -4                                                                          D.sub.4 -5                                                                          D.sub.4 -6                 __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          --   --   H.sub.2                                                                             0.375N                                                                              0.374N                                                                              0.375N                                                                              0.4% 1.0% 1.0%                       tions                                                                               agent                 NaOH NaOH NaOH Hydra-                                                                              Formal-                                                                             Sodium                     of                                        zine dehyde                                                                              boro-                      treat-                                              hydride                    for  Temper-                                                                               --   --   650  30   50   100  20   60   60                         reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              --   --   6.0  1.0  1.0  1.0  1.0  1.0  1.0                             (ata)                                                                          Time (hrs)                                                                            --   --   12.0 3.0  6.0  3.0  3.0  3.0  3.0                             Post-treat-                                                                           --   --   --   Water washing: 100° C.,                                                                --   --   --                              ment                  2 hrs.                                                                         Drying: 100° C., 16 hrs.                     Elimina-                                                                             Carbo-                                                                               --   --   100  10   41   56    0    0    0                         tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             --   --   29   30   80   94   72   71   90                         materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43   20                                                                               19      23   29   36   23   26   26                          (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         91   --                                                                               --      --   145  109  270  264  270                        required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________                 Reactivated                                                        Catalyst    D.sub.4 -7                                                                          D.sub.4 -8                                                                          D.sub.4 -9                                                                          D.sub.4 -10                                                                         D.sub.4 -11                                                                         D.sub.4 -12                                                                         D.sub.4l -13                                                                        D.sub.4 -14                                                                         D.sub.4 -15                __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.375N                                                                              0.375N                                                                              0.375N                                                                              0.1N 0.375N                                                                              0.375N                                                                              0.5% 0.3% 0.3%                       tions                                                                               agent  Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                                                                        Sr(OH).sub.2                                                                        Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                                                                        Sr(OH).sub.2                                                                        Formal-                                                                             Sodium                                                                              Lithium                    of                                        dehyde                                                                              boro-                                                                               aluminum                   treat-                                         hydride                                                                             hydride                    ment                                                                           for  Temper-                                                                               100  100  100  100  80   100  20   20   20                         reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                             (ata)                                                                          Time (hrs)                                                                            3.0  3.0  3.0  3.0  3.0  1.0  3.0  3.0  3.0                             Post-treat-                                                                           Water washing: 100° C., 2 hrs.                                                                        Water washing: 75° C., 3                                                hrs.                                      ment   Drying: 100° C., 16 hrs.                                                                              Drying: 100° C., 16                                                     hrs.                                 Elimina-                                                                            Carbo- 54   51   50   44   49   46    0    0    0                         tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             91   89   86   77   80   79   56   70   51                         materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      36   35   35   32   32   31   23   23   26                          (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         111  114  119  123  126  129  274  278  260                        required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________                 Reactivated                                                        Catalyst    D.sub.4 -16                                                                         D.sub.4 -17                                                                          D.sub.4 -18                                             __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.7% 2.0% 0.3%                                                     tions                                                                               agent  Sodium                                                                              Sodium                                                                              Glucose                                                  of          tart-                                                                               formate                                                       treat-      rate                                                               ment                                                                           for  Temper-                                                                               20   20   20                                                       reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0  1.0  1.0                                                           (ata)                                                                          Time (hrs)                                                                            3.0  3.0  3.0                                                           Post-treat-                                                                           Water washing: 75° C., 3 hrs.                                    ment   Drying: 100° C., 16 hrs.                                    Elimina-                                                                            Carbo-  0    0    0                                                       tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             49   57   52                                                       materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      26   25   23                                                        (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         264  264  270                                                      required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 8

The reactivated catalysts as obtained in Example 7 (Catalysts D₄ -1 to D₄ -3, D₄ -8 and D₄ -10 to D₄ -18) were each subjected to further treatment for reactivation under the conditions as shown in Table 5. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 7. The results are shown in Table 5.

As seen from Table 5, the catalysts (E₅ -1 to E₅ -19) reactivated in two steps are much more recovered in catalytic activity than the catalysts (D₄ -1 to D₄ -3, D₄ -8 and D₄ -10 to D₄ -18) reactivated in one step.

                                      Table 5                                      __________________________________________________________________________     Catalyst    E.sub.5 -1                                                                           E.sub.5 -2                                                                          E.sub.5 -3                                                                          E.sub.5 -4                                                                          E.sub.5 -5                                                                          E.sub.5 -6                                                                          E.sub.5 -7                                                                          E.sub.5 -8                                                                          E.sub.5 -9                                                                          E.sub.5 -10          Catalyst used                                                                              D.sub.4 -1                                                                           D.sub.4 -3                                                                          D.sub.4 -8                                                                          D.sub.4 -8                                                                          D.sub.4 -10                                                                         D.sub.4 -11                                                                         D.sub.4 -12                                                                         D.sub.4 -13                                                                         D.sub.4 -13                                                                         D.sub.4              __________________________________________________________________________                                                               -14                  Condi-                                                                              Reactivating                                                                          1.0%  0.4% 0.5% 0.5% 0.5% 1.0% 0.3% 0.375N                                                                              0.1N 0.375N               tions                                                                               agent  Sodium                                                                               Hydra-                                                                              Formal-                                                                             Formal-                                                                             Formal-                                                                             Hydra-                                                                              Sodium                                                                              NaOH NaOH KOH                  of          boro- zine dehyde                                                                              dehyde                                                                              dehyde                                                                              zine boro-                               treat-      hydride                        hydride                             ment                                                                           for  Temper-                                                                               60    20   20   60   20   60   20   100  100  80                   reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                       (ata)                                                                          Time (hrs)                                                                            3.0   3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0                  Post-treat- Water washing: 75° C., 3 hrs.                                                                               Water washing:                                                                 100° C.,                ment        Drying: 100° C., 16 hrs.        2 hrs.                                                                      Drying: 100° C.,                                                        16 hrs.                        Elimina-                                                                            Carbo- 10    56   51   51   44   49   46   54   44   52                   tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             86    96   95   97   89   96   90   86   80   85                   materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      36    41   41   41   36   41   35   41   36   36                    (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         109   93   97   93   106  97   116  95   102  106                  required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________     Catalyst    E.sub.5 -11                                                                          E.sub.5 -12                                                                         E.sub.5 -13                                                                          D.sub.5 -14                                                                         E.sub.5 -15                                                                          E.sub.5 -16                                                                          E.sub.5 -17                                                                         E.sub.5 -18                                                                          D.sub.5 -19           Catalyst used                                                                              D.sub.4 -1                                                                           D.sub.4 -2                                                                          D.sub.4 -10                                                                          D.sub.4 -11                                                                         D.sub.4 -12                                                                          D.sub.4 -15                                                                          D.sub.4 -16                                                                         D.sub.4 -17                                                                          D.sub.4 -18           __________________________________________________________________________     Condi-                                                                              Reactivating                                                                           0.7% 0.3% 0.3%  2.0% 0.3%  0.1N  0.1N 0.375N                                                                               0.375N                tions                                                                               agent  Sodium                                                                               Glucose                                                                             Lithium                                                                              Sodium                                                                              Lithium                                                                              NaOH  Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                                                                         Sr(OH).sub.2          of          tart-      aluminum                                                                             formate                                                                             aluminum                                     treat-      rate       hydride    hydride                                      ment                                                                           for  Temper-                                                                               20    20   20    20   20    100   100  80    100                   reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0  1.0   1.0  1.0   1.0   1.0  1.0   1.0                        (ata)                                                                          Time (hrs)                                                                            3.0   3.0  3.0   3.0  3.0   3.0   3.0  3.0   1.0                   Post-treat- Water washing: 75° C., 3 hrs.                                                                       Water washing: 100° C., 2                                               hrs.                                   ment        Drying: 100° C., 16 hrs.                                                                            Drying: 100° C., 16 hrs.        Elimina-                                                                            Carbo- 10    41   44    49   46    47    44   49    46                    tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             65    91   89    91   90    90    88   91    90                    materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      32    37   40    37   36    41    40   37    35                     (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         123   102  98    102  106   96    100  102   112                   required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 9

The reactivated catalyst obtained in Example 7 (Catalyst D₄ -13) was treated with a 0.1 N aqueous solution of sodium hydroxide at 100° C. under 1 atm. (absolute) for 3 hours, washed with water at 100° C. for 2 hours and dried at 100° C. for 16 hours. Then, the resulting catalyst was again subjected to treatment with a 0.5% aqueous solution of formaldehyde at 20° C. under 1 atm. (absolute) for 3 hours and treatment with a 0.1 N aqueous solution of sodium hydroxide at 100° C. under 1 atm. (absolute) for 3 hours, followed by washing with water at 100° C. for 2 hours and drying at 100° C. for 16 hours. The thus reactivated catalyst was used for steam-reforming under the same conditions as stated in Example 7. The results are as follows: elimination percentage of poisonous materials: carbonaceous materials, 80 %; sulfurous material, 100%. Specific surface area: 42 m² /g-Ru. Amount of catalyst required for reaction: 92 ml.

As seen from the above results, the repeating treatments with a reducing substance and with an inorganic alkaline substance are quite effective for reactivation of the catalyst.

EXAMPLE 10

The reactivated catalyst obtained in Example 7 (Catalyst D₄ -17) was treated with a 0.375 N aqueous solution of barium hydroxide at 80° C. under 1 atm. (absolute) for 3 hours, washed with water at 100° C. for 2 hours and dried at 100° C. for 16 hours. Then, the resulting catalyst was again subjected to treatment with a 2.0% aqueous solution of sodium formate at 20° C. under 1 atm. (absolute) for 3 hours and treatment with a 0.375 N aqueous solution of barium hydroxide at 80° C. under 1 atm. (absolute) for 3 hours, followed by washing with water at 100° C. for 2 hours and drying at 100° C. for 16 hours. The thus reactivated catalyst was used for steam-reforming under the same conditions as stated in Example 7. The results are as follows: elimination percentage of poisonous materials: carbonaceous materials, 76%; sulfurous material, 100%. Specific surface area: 42 m² /g-Ru. Amount of catalyst required for reaction: 92 ml.

As seen from the above results, the repeating treatments with an inorganic alkaline substance and with a reducing substance are quite effective for reactivation of the catalyst.

EXAMPLE 11

The reactivated catalysts obtained in Example 4 (Catalyst E₃ -5) and in Example 4 (Catalyst E₃ -7) were each reused for steam-reforming under the same conditions as shown in Example 3. The results are shown in Table 6, from which it is understood that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₂) in depression of the catalytic activity and their catalytic activity, particularly that of Catalyst E₃ -5, is nearly equal to the catalytic activity of the fresh catalyst.

                  Table 6                                                          ______________________________________                                         Catalyst            A.sub.2  E.sub.3 -5                                                                              E.sub.3 -7                               ______________________________________                                         Amount of catalyst                                                                         Start        92       95    102                                    required for                                                                   reaction (ml)                                                                              600 hours   164      171    183                                                1200 hours  221      232    250                                    ______________________________________                                    

EXAMPLE 12

The reactivated catalysts obtained in Example 4 (Catalyst E₃ -13) and in Example 6 were each reused for steam-reforming under the same conditions as shown in Example 3. The results are shown in Table 7, from which it is seen that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₂) in depression of the catalytic activity and their catalytic activity, particularly that of the reactivated catalyst obtained in Example 6 is nearly equal to the catalytic activity of the fresh catalyst.

                  Table 7                                                          ______________________________________                                                                            Obtained in                                 Catalyst          A.sub.2 E.sub.3 -13                                                                             Example 6                                   ______________________________________                                         Amount of catalyst                                                                         Start      92     100     93                                       required for                                                                   reaction (ml)                                                                              600 hours 164     179    166                                                   1200 hours                                                                               221     242    224                                       ______________________________________                                    

EXAMPLE 13

The reactivated catalysts obtained in Example 8 (Catalyst E₅ -8) and in Example 9 were each reused for steam-reforming under the same conditions as shown in Example 7. The results are shown in Table 8, from which it is seen that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₄) in depression of the catalytic activity.

                  Table 8                                                          ______________________________________                                                                            Obtained in                                 Catalyst          A.sub.4 E.sub.5 -8                                                                              Example 9                                   ______________________________________                                         Amount of catalyst                                                                         Start      91      95     92                                       required for                                                                   reaction (ml)                                                                              200 hours 156     167    159                                                   400 hours 222     238    226                                       ______________________________________                                    

EXAMPLE 14

The reactivated catalysts obtained in Example 8 (Catalyst E₅ -16) and in Example 10 were each reused for steam-reforming under the same conditions as shown in Example 7. The results are shown in Table 9, from which it is seen that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₄) in depression of the catalytic activity.

                  Table 9                                                          ______________________________________                                                                            Obtained in                                 Catalyst          A.sub.4 E.sub.5 -16                                                                             Example 10                                  ______________________________________                                         Amount of catalyst                                                                         Start      91      96     92                                       required for                                                                   reaction (ml)                                                                              200 hours 156     166    160                                                   400 hours 222     235    229                                       ______________________________________                                    

EXAMPLE 15

A catalyst comprising 2.0% of ruthenium and 0.1% of chromium oxide deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (hereinafter referred to as "Catalyst A₁₀ ") (325 ml) was charged into a tubular reactor of 1 inch in diameter, and a gaseous mixture comprising naphtha (content of sulfur, 2 ppm; final boiling point, 168° C.), steam, hydrogen, methane and carbon oxides was fed therein to effect continuously steam-reforming reaction for 1500 hours under the following conditions:

Temperature of reactor: inlet, 450° C., outlet, 524° C.;

Space velocity: 2000 (l/hr);

Ratio of steam/hydrocarbon: 0.9 (number of oxygen atoms per one carbon atom in the feeding gaseous mixture);

Pressure: 13 atm. (absolute)

After 1500 hours, the resultant catalyst (hereinafter referred to as "Catalyst B₁₀ ") was treated under the conditions as shown in Table 10 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 10.

As seen from Table 10, the reactivation treatment with gaseous materials is effective for elimination of carbonaceous materials, but removal of sulfurous materials is insufficient and the dispersibility can be hardly recovered so that recovery of the catalytic activity is scarcely observed (Catalysts C₁₀ -1 to C₁₀ -5). In the case of treatment with an inorganic alkaline substance, elimination of sulfurous materials and recovery of the dispersibility (as well as recovery of the catalytic activity) are good.

                                      Table 10                                     __________________________________________________________________________                             Reactivated                                            Catalyst    A.sub.10                                                                             B.sub.10                                                                             C.sub.10 -1                                                                        C.sub.10 -2                                                                         C.sub.10 -3                                                                         C.sub.10 -4                                                                         C.sub.10 -5                                                                         D.sub.10 -1                                                                         D.sub.10 -2                                                                         D.sub.10             __________________________________________________________________________                                                               -3                   Condi-                                                                              Reactivating                                                                          --    --    H.sub.2                                                                            H.sub.2 :H.sub.2 O                                                                  H.sub.2 O:N.sub.2                                                                   O.sub.2 :N.sub.2                                                                    O.sub.2 :H.sub.2 O:                                                                 0.375N                                                                              0.375N                                                                              0.375N               tions                                                                               agent (*)              (=1:1                                                                               (=3:1                                                                               (=21:                                                                               N.sub.2 (=10:                                                                       NaOH Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2         of                          by mol)                                                                             by mol)                                                                             79 by                                                                               50:40 by                            treat-                                volume)                                                                             volume)                             ment                                                                           for  Temper-                                                                               --    --    600 600  650  500  600  100  100  100                  reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              --    --    6.0 6.0  6.0  6.0  6.0  1.0  1.0  1.0                       (ata)                                                                          Time (hrs)                                                                            --    --    6.0 6.0  12.0 5.0  10.0 1.5  3.0  3.0                  Post-treat- --    --    --  --   --   --   --   Water washing:                                                                 100° C.,                ment                                               2 hrs.                                                                      Drying: 100° C.,                                                        16 hrs.                        Elimina-                                                                            Carbo- --    --    78  80   100  100  100  55   54   50                   tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             --    --    21  28   32   40   38   95   93   87                   materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43    20    19  19   19   17   18   35   36   33                    (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         52.5  --    --  --   --   --   --   63   64   66                   required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________      Note:                                                                          (*) In case of Catalysts C.sub.10 -1 to C.sub.10 -5, the treatment was         carried out with a space velocity of 2500 (lhr).                         

    Reactivated                                                                                                           Catalyst    D.sub.10 -4                                                                          D.sub.10              __________________________________________________________________________                                                              -5                                                           Condi-                                                                               Reactivating                                                                         0.375N                                                                               0.375N                                                       tions                                                                               agent  NaOH  NaOH                                                         of                                                                             treat-                                                                         ment                                                                           for  Temper-                                                                               50    30                                                           reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0                                                               (ata)                                                                          Time (hrs)                                                                            6.0   10.0                                                               Post-treat-                                                                          Water washing:                                                                 100° C.,                                                          ment     2 hrs.                                                                      Drying: 100°                                                            C., 16 hrs.                                                        Elimina-                                                                             Carbo-                                                                               41    40                                                           tion per-                                                                            naceous                                                                  centage                                                                              materials                                                                of                                                                             poisonous                                                                            Sulfurous                                                                            78    75                                                           materials                                                                            materials                                                                (%)                                                                            Specific surface                                                                           28ea  28                                                            (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         85    --                                                           required for reac-                                                             tion (ml)                               __________________________________________________________________________

EXAMPLE 16

The reactivated catalysts as obtained in Example 15 (Catalysts C₁₀ -1, C₁₀ -2 and C₁₀ -5) were each subjected to further treatment for reactivation under the conditions as shown in Table 11. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 15. The results are shown in Table 11.

As seen from Table 11, the catalysts (E₁₁ -1 to E₁₁ -6) reactivated in two steps are much recovered in catalytic activity.

                                      Table 11                                     __________________________________________________________________________     Catalyst    E.sub.11 -1                                                                         E.sub.11 -2                                                                         E.sub.11 -3                                                                         E.sub.11 -4                                                                         E.sub.11 -5                                                                         E.sub.11 -6                                                                         E.sub.11 -7                                                                         E.sub.11 -8                     Catalyst used                                                                              C.sub.10 -1                                                                         C.sub.10 -1                                                                         C.sub.10 -1                                                                         C.sub.10 -1                                                                         C.sub.10 -2                                                                         C.sub.10 -5                                                                         C.sub.10 -1                                                                         C.sub.10 -1                     __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.375N                                                                              0.375N                                                                              0.375N                                                                              0.375N                                                                              0.1N 0.375N                                                                              0.375N                                                                              0.375N                          tions                                                                               agent  NaOH NaOH Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                                                                        NaOH NaOH NaOH NaOH                            of                                                                             treat-                                                                         ment                                                                           for  Temper-                                                                               50   80   100  100  100  80   30   30                              reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                                  (ata)                                                                          Time (hrs)                                                                            3.0  1.5  1.5  2.0  1.5  1.5  10.0 3.0                             Post-treat- Water washing: 100° C., 2 hrs.                              ment        Drying: 100° C., 16 hrs.                                    Elimina-                                                                            Carbo- 81   86   85   83   83   100  80   80                              tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             83   96   94   88   90   97   80   48                              materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      31   38   37   35   37   38   28   23                               (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         78   58   61   63   61   58   --   --                              required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 17

The reactivated catalysts as obtained in Example 16 (Catalysts E₁₁ -1, E₁₁ -7 and E₁₁ -8) were each subjected to further treatment for reactivation under the conditions as shown in Table 12. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 15. The results are shown in Table 12.

As seen from Table 12, the catalysts (F₁₂ -1 to F₁₂ -11) reactivated in three steps are much recovered in catalytic activity.

                                      Table 12                                     __________________________________________________________________________     Catalyst    F.sub.12 -1                                                                        F.sub.12 -2                                                                         F.sub.12 -3                                                                         F.sub.12 -4                                                                          F.sub.12 -5                                                                        F.sub.12 -6                                                                        F.sub.12 -7                                                                        F.sub.12 -8                                                                         F.sub.12 -9                                                                         F.sub.12 -10                                                                        F.sub.12 -11        Catalyst used                                                                              E.sub.11 -1                                                                        E.sub.11 -1                                                                         E.sub.11 -1                                                                         E.sub.11 -1                                                                          E.sub.11 -1                                                                        E.sub.11 -7                                                                        E.sub.11 -7                                                                        E.sub.11 -7                                                                         E.sub.11 -7                                                                         E.sub.11 -7                                                                         E.sub.11            __________________________________________________________________________                                                                -8                  Condi-                                                                              Reactivating                                                                          0.4%                                                                               0.5% 0.3% 0.3%  0.3%                                                                               0.4%                                                                               0.5%                                                                               0.3% 0.7% 2.0% 1.0%                tions                                                                               agent  Hydra-                                                                             Formal-                                                                             Sodium                                                                              Lithium                                                                              Glu-                                                                               Hydra-                                                                             For-                                                                               Sodium                                                                              Sodium                                                                              So-  Hydra-              of          zine                                                                               dehyde                                                                              boro-                                                                               aluminum                                                                             cose                                                                               zine                                                                               de- boro-                                                                               tart-                                                                               for- zine                treat-               hydride                                                                             hydride       hyde                                                                               hydride                                                                             rate mate                     ment                                                                           for  Temper-                                                                               20  20   20   20    20  20  20  20   20   20   60                  reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0 1.0  1.0  1.0   1.0 1.0 1.0 1.0  1.0  1.0  1.0                      (ata)                                                                          Time (hrs)                                                                            3.0 3.0  3.0  3.0   3.0 3.0 3.0 3.0  3.0  3.0  3.0                      Post-treat-                                                                           Water washing: 75° C., 3 hrs.                                    ment   Drying: 100° C., 16 hrs.                                    Elimina-                                                                            Carbo- 81  81   81   81    81  80  80  80   80   80   80                  tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             96  90   95   92    92  92  87  90   91   93   94                  materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      41  40   40   40    40  37  36  35   36   36   39                   (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         53  55   56   53    56  60  61  63   61   61   56                  required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 18

The reactivated catalysts obtained in Example 16 (Catalyst E₁₁ -2) and in Example 17 (Catalyst F₁₂ -1) were each reused for steam-reforming under the same conditions as shown in Example 15. The results are shown in Table 13, from which it is seen that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₁₀) in depression of the catalytic activity and their catalytic activity, particularly that of Catalyst F₁₂ -1 is nearly equal to the catalytic activity of the fresh catalyst.

                  Table 13                                                         ______________________________________                                         Catalyst          A.sub.10 E.sub.11 -2                                                                             F.sub.12 -1                                ______________________________________                                         Amount of catalyst                                                                         Start     52.5     58     53                                       required for                                                                   reaction (ml)                                                                              300 hours 123.5    139.5  125                                                  600 hours 183      208.5  186                                                  900 hours 252      289    257                                      ______________________________________                                    

EXAMPLE 19

A catalyst comprising 2.6% of ruthenium and 0.1% of chromium oxide deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (hereinafter referred to as "Catalyst A₁₄ ") (325 ml) was charged into a tubular reactor of 1 inch in diameter, and a gaseous mixture comprising naphtha (content of sulfur, 2 ppm; final boiling point, 168° C.), steam, hydrogen, methane and carbon oxides was fed therein to effect continuously steam-reforming reaction for 2400 hours under the following conditions:

Temperature of reactor: inlet, 400° C., outlet, 517° C.;

Space velocity: 1500 (l/hr);

Ratio of steam/hydrocarbon: 0.7 (number of oxygen atoms per one carbon atom in the feeding gaseous mixture);

Pressure: 13 atm. (absolute

After 2400 hours, the resultant catalyst (hereinafter referred to as "Catalyst B₁₄ ") was treated under the conditions as shown in Table 14 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 14.

As seen from Table 14, the reactivation treatment with gaseous materials is effective for elimination of carbonaceous materials, but removal of sulfurous materials is insufficient and the dispersibility can be hardly recovered so that recovery of the catalytic activity is scarcely observed (Catalysts C₁₄ -1 to C₁₄ -5). In the case of treatment with an inorganic alkaline substance, elimination of sulfurous materials and recovery of the dispersibility (as well as recovery of the catalytic activity) are good.

                                      Table 14                                     __________________________________________________________________________                           Reactivated                                              Catalyst    A.sub.14                                                                            B.sub.14                                                                            C.sub.14 -1                                                                         C.sub.14 -2                                                                         C.sub.14 -3                                                                         C.sub.14 -4                                                                         C.sub.14 -5                                                                         D.sub.14 -1                                                                         D.sub.14 -2                                                                         D.sub.14              __________________________________________________________________________                                                              -3                    Condi-                                                                              Reactivating                                                                          --   --   H.sub.2                                                                             H.sub.2 :H.sub.2 O                                                                  H.sub.2 O:N.sub.2                                                                   O.sub.2 :N.sub.2                                                                    O.sub.2 :H.sub.2 O:                                                                 0.375N                                                                              0.375N                                                                              0.375N                tions                                                                               agent (*)             (=1:1                                                                               (=3:1                                                                               (=21:                                                                               N.sub.2 (=10:                                                                       NaOH NaOH NaOH                  of                         by mol)                                                                             by mol)                                                                             79 by                                                                               50:40 by                             treat-                               volume)                                                                             volume)                              ment                                                                           for  Temper-                                                                               --   --   600  600  650  500  600  30   30   50                    reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              --   --   6.0  6.0  6.0  6.0  6.0  1.0  1.0  1.0                        (ata)                                                                          Time (hrs)                                                                            --   --   6.0  6.0  12.0 5.0  10.0 3.0  10.0 6.0                   Post-treat- --   --   --   --   --   --   --   Water washing: 100°                                                     C.,                             ment                                              2 hrs.                                                                      Drying: 100° C., 16                                                     hrs.                            Elimina-                                                                            Carbo- --   --   75   78   100  100  100  12   41   43                    tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             --   --   19   25   30   37   35   32   72   78                    materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43   20   19   19   19   17   18   21   27   28                     (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         92   --   --   --   --   --   --   --   --   147                   required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________      Note:                                                                          (*) In case of Catalysts C.sub.14 -1 to C.sub.14 -5, the treatment was         carried out with a space velocity of 2500 (l/hr).                        

    Reactivated                                                                    Catalyst    D.sub.14 -4                                                                         D.sub.14 -5                                                                         D.sub.14 -6                                                                         D.sub. 14 -7                                                                        D.sub.14 -8                                                                         D.sub.14 -9                               __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          0.375N                                                                              0.375N                                                                              0.375N                                                                              0.1N 0.375N                                                                              0.375N                                    tions                                                                               agent  NaOH Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                                                                        NaOH Na.sub.2 CO.sub.3                                                                   Ba(OH).sub.2                              of                                                                             treat-                                                                         ment                                                                           for  Temper-                                                                               100  100  100  100  80   100                                       reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0  1.0  1.0  1.0  1.0  1.0                                            (ata)                                                                          Time (hrs)                                                                            3.0  3.0  3.0  3.0  3.0  1.5                                       Post-treat- Water washing: 100° C., 2 hrs.                                          ment                          Drying: 100° C., 16                                                     hrs.                                 Elimina-                                                                            Carbo- 52   51   47   40   44   45                                        tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             90   88   82   75   77   76                                        materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      34   34   32   30   30   29                                         (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         110  112  116  120  122  127                                       required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 20

The reactivated catalysts as obtained in Example 19 (Catalysts D₁₄ -7 to D₁₄ -9) were each subjected to further treatment for reactivation under the conditions as shown in Table 15. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 19. The results are shown in Table 15.

As seen from Table 15, the catalysts (E₁₅ -1 to E₁₅ -5) reactivated in two steps are much recovered in catalytic activity.

                  Table 15                                                         ______________________________________                                         Catalyst    E.sub.15 -1                                                                            E.sub.15 -2                                                                            E.sub.15 -3                                                                           E.sub.15 -4                                                                           E.sub.15 -5                          Catalyst used                                                                              D.sub.14 -7                                                                            D.sub.14 -7                                                                            D.sub.14 -7                                                                           D.sub.14 -8                                                                           D.sub.14 -9                          ______________________________________                                         Condi- Reac-    H.sub.2 H.sub.2 :                                                                            O.sub.2 :H.sub.2 O:                                                                   H.sub.2                                                                               H.sub.2 :                                 tivating         H.sub.2 O           H.sub.2 O                          tions  agent (*)        (=1:1 N.sub.2 (=10: (=1:1                              of                      by    50:40 by      by                                 treat-                  mol)  volume)       mol)                               ment                                                                           for    Temper-  600     600   600    650    650                                reacti-                                                                               ature                                                                   vation (° C.)                                                                  Pressure 6.0     6.0   6.0    6.0    6.0                                       (ata)                                                                          Time     6.0     6.0   10.0   12.0   12.0                                      (hrs)                                                                          Post-    --      --    --     --     --                                        treat-                                                                         ment                                                                    Elimina-                                                                              Carbo-   85      87    100    100    100                                tion per-                                                                             naceous                                                                 centage                                                                               materials                                                               of                                                                             poisonous                                                                             Sul-     80      81    84     81     82                                 materials                                                                             furous                                                                         materials                                                               (%)                                                                            Specific    31      31      30     30      30                                  surface area                                                                    (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         105     105     110    110    112                                  required for reac-                                                             tion (ml)                                                                      ______________________________________                                          Note:                                                                          (*) In case of Catalysts E.sub.15 -1 to E.sub.15 -5, the treatment was         carried out with a space velocity of 2500 (l/hr).                        

EXAMPLE 21

The reactivated catalysts as obtained in Example 19 (Catalysts D₁₄ -1 to D₁₄ -4, D₁₄ -8 and D₁₄ -9) were each subjected to further treatment for reactivation under the conditions as shown in Table 16. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 19. The results are shown in Table 16.

As seen from Table 16, the catalysts (E₁₆ -1 to E₁₆ -10) reactivated in two steps are much recovered in catalytic activity.

                                      Table 16                                     __________________________________________________________________________     Catalyst    E.sub.16 -1                                                                         E.sub.16 -2                                                                         E.sub.16 -3                                                                          E.sub.16 -4                                                                         E.sub.16 -5                                                                         E.sub.16 -6                                                                         E.sub.16 -7                                                                         E.sub.16 -8                                                                         E.sub.16 -9                                                                         E.sub.16 -10         Catalyst used                                                                              D.sub.14 -1                                                                         D.sub.14 -2                                                                         D.sub.14 -3                                                                          D.sub.14 -3                                                                         D.sub.14 -3                                                                         D.sub.14 -4                                                                         D.sub.14 -8                                                                         D.sub.14 -8                                                                         D.sub.14 -9                                                                         D.sub.14 -9          Condi-                                                                             Reactivating                                                                           1.0% 0.4% 0.3%  0.5% 0.3% 0.3% 0.5% 0.7% 0.4% 2.0%                 tions                                                                              agent   Hydra-                                                                              Hydra-                                                                              Lithium                                                                              Formal-                                                                             Sodium                                                                              Glucose                                                                             Formal-                                                                             Sodium                                                                              Hydra-                                                                              Sodium               of          zine zine aluminum                                                                             dehyde                                                                              boro-     dehyde                                                                              tart-                                                                               zine formate              treat-                hydride    hydride        rate                           ment                                                                           for Temper- 60   20   20    20   20   20   20   20   20   20                   reacti-                                                                            ature (° C.)                                                        vation                                                                             Pressure                                                                               1.0  1.0  1.0   1.0  1.0  1.0  1.0  1.0  1.0  1.0                      (ata)                                                                          Time (hrs)                                                                             3.0  3.0  3.0   3.0  3.0  3.0  3.0  3.0  3.0  3.0                  Post-treat- Water washing: 75° C., 3 hrs.                               ment        Drying: 100° C., 16 hrs.                                    Elimina-                                                                             Carbo-                                                                                12  41   43    43   43   52   44   44   45   45                   tion per-                                                                            naceous                                                                  centage                                                                              materials                                                                of                                                                             poisonous                                                                            Sulfurous                                                                            89   91   93    93   93   97   90   88   92   90                   materials                                                                            materials                                                                (%)                                                                            Specific surface area                                                                      34   36   36    36   34   40   36   36   36   36                   (m.sup.2 /g-Ru)                                                                Amount of catalyst                                                                         108  110  102   106  108  95   106  106  102  102                  required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 22

The reactivated catalysts as obtained in Example 21 (Catalysts E₁₆ -1, E₁₆ -3 and E₁₆ -5 to E₁₆ -7) were each subjected to further treatment for reactivation under the conditions as shown in Table 17. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 15. The results are shown in Table 17.

As seen from Table 17, the catalysts (F₁₇ -1 to F₁₇ -5) reactivated in three steps are much recovered in catalytic activity.

                                      Table 17                                     __________________________________________________________________________     Catalyst    F.sub.17 -1                                                                         F.sub.17 -2                                                                         F.sub.17 -3                                                                         F.sub.17 -4                                                                         F.sub.17 -5                                    Catalyst used                                                                              E.sub.16 -1                                                                         E.sub.16 -3                                                                         E.sub.16 -5                                                                         E.sub.16 -6                                                                         E.sub.16 -7                                    __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          H.sub.2                                                                             H.sub.2                                                                             H.sub.2 :H.sub.2 O                                                                  H.sub.2 O:N.sub.2                                                                   O.sub.2 :H.sub.2 O:N.sub.2                     tions                                                                               agent (*)        (=1:1                                                                               (=3:1                                                                               (=10:50:40                                     of                    by mol)                                                                             by mol)                                                                             by volume)                                     treat-                                                                         ment                                                                           for  Temper-                                                                               650  600  600  650  600                                            reacti-                                                                             ature (° C.)                                                            Pressure                                                                              6.0  6.0  6.0  6.0  6.0                                                 (ata)                                                                          Time (hrs)                                                                            12.0 6.0  6.0  12.0 10.0                                                Post-treat-                                                                           --   --   --   --   --                                                  ment                                                                      Elimina-                                                                            Carbo- 100  86   87   100  100                                            tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             96   96   96   97   94                                             materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      35   37   35   40   37                                              (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         100  96   102  93   98                                             required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________      (*) In case of Catalysts F.sub.17 -1 to F.sub.17 -5, the treatment was         carried out with a space velocity of 2500 (1/hr).                        

EXAMPLE 23

The reactivated catalysts obtained in Example 20 (Catalyst E₁₅ -1) and in Example 22 (Catalyst F₁₇ -4) were each reused for steam-reforming under the same conditions as shown in Example 19. The results are shown in Table 18, from which it is seen that the reactivated catalysts show the similar behavior to the fresh catalyst (Catalyst A₁₄) in depression of the catalytic activity and their catalytic activity, particularly that of Catalyst F₁₇ -4, is nearly equal to the catalytic activity of the fresh catalyst.

                  Table 18                                                         ______________________________________                                         Catalyst           A.sub.14                                                                               E.sub.15 -1                                                                            F.sub.17 -4                                 ______________________________________                                         Amount of catalyst                                                                         Start       92     105    93                                       required for                                                                   reaction (ml)                                                                              600 hours  164     191   168                                                   1200 hours 221     260   227                                       ______________________________________                                    

EXAMPLE 24

A catalyst comprising 2% of ruthenium deposited on spheroidal particles of alumina of 4 mm in diameter (hereinafter referred to as "Catalyst A₁₈ ") (6700 ml) was charged into a tubular reactor of 5 inch in diameter, and methanol and steam were fed therein to effect continuously steam-reforming reaction for 2000 hours under the following conditions:

Temperature of reactor: inlet, 580° C., outlet, 620° C.;

Space velocity: 15800 (l/hr.);

Ratio of steam/methanol: 1.5 (by mol);

Pressure: 6 atm. (absolute)

After 2000 hours, the catalyst (hereinafter referred to as "Catalyst B₁₈ ") was treated under the same conditions as shown in Table 18 for reactivation. The reactivated catalyst was reused in steam-reforming reaction under the same conditions as mentioned above. The results are shown in Table 18.

As seen from Table 18, treatment with an inorganic alkaline substance or a reducing substance shows recovery of the catalytic activity.

                                      Table 18                                     __________________________________________________________________________                       Reactivated                                                  Catalyst    A.sub.18                                                                          B.sub.18                                                                          D.sub.18 -1                                                                          D.sub.18 -2                                                                          D.sub.18 -3                                                                          D.sub.18 -4                                __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          -- -- 0.375N                                                                               0.375N                                                                               1.0%  0.3%                                       tions                                                                               agent        NaOH  NaOH  Hydra-                                                                               Glucose                                    of                            zine                                             treat-                                                                         ment                                                                           for  Temper-                                                                               -- -- 30    100   60    20                                         reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              -- -- 1.0   1.0   1.0   1.0                                             (ata)                                                                          Time (hrs)                                                                            -- -- 3.0   3.0   3.0   3.0                                             Post-treat-                                                                           -- -- Water washing:                                                                             Water washing:                                        ment         100° C., 2 hrs.                                                                     75° C., 3 hrs.                                              Drying: 100° C., 16 hrs.                                                            Drying: 100  C., 16 hrs.                         Elimina-                                                                            Carbo- -- -- 12    53     0     0                                         tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             -- -- --    --    --    --                                         materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                       43                                                                               17 20    34    23    23                                          (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         1.3                                                                               -- --    1.6   3.8   4.0                                        required for reac-                                                             tion (1)                                                                       __________________________________________________________________________

EXAMPLE 25

The reactivated catalysts as obtained in Example 24 (Catalysts D₁₈ -1 to D₁₈ -4) were each subjected to further treatment for reactivation under the conditions as shown in Table 19. The thus reactivated catalysts were each reused for continuous steam-reforming under the same conditions as shown in Example 24. The results are shown in Table 19.

As seen from Table 19, the catalysts (E₁₉ -1 to E₁₉ -4) reactivated in two steps are much more recovered in catalytic activity than the catalysts (D₁₈ -1 to D₁₈ -4) reactivated in one step.

                                      Table 19                                     __________________________________________________________________________     Catalyst    E.sub.19 -1                                                                          E.sub.19 -2                                                                          E.sub.19 -3                                                                          E.sub.19 -4                                      Catalyst used                                                                              D.sub.18 -1                                                                          D.sub.18 -2                                                                          D.sub.18 -3                                                                          D.sub.18 -4                                      __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          1.0%  0.3%  0.375N                                                                               0.375N                                           tions                                                                               agent  Hydra-                                                                               Sodium                                                                               NaOH  NaOH                                             of          zine  boro-                                                        treat-            hydride                                                      ment                                                                           for  Temper-                                                                               60    20    100   80                                               reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0   1.0   1.0                                                   (ata)                                                                          Time (hrs)                                                                            3.0   3.0   3.0   3.0                                              Post-treat- Water washing: 75° C.,                                                              Water washing: 100° C.,                         ment           3 hrs.   (   2) hrs.                                                        Drying: 100° C., 16 hrs.                                                            Drying: 100° C., 16 hrs.                        Elimina-                                                                            Carbo- 12    52    52    50                                               tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             --    --    --    --                                               materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      34    40    41    38                                                (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         1.5   1.4   1.3   1.4                                              required for reac-                                                             tion (1)                                                                       __________________________________________________________________________

EXAMPLE 26

A catalyst comprising 2.0% of ruthenium deposited on spheroidal particles of alumina of 4 mm in diameter as a carrier material (hereinafter referred to as "Catalyst A₂₀ ") (290 ml) was charged into a tubular reactor of 1 inch in diameter, and methane (content of sulfur, 2 ppm) and air were fed therein to effect continuously partial oxidation for 2500 hours under the following conditions:

Temperature of reactor: inlet, 310° C., outlet, 700° C.;

Space velocity: 17500 (l/hr.);

Ratio of air/methane: 2.37 (by mol);

Pressure: 1 atm. (absolute)

After 2500 hours, the resultant catalyst (hereinafter referred to as "Catalyst B₂₀ ") was treated under the conditions as shown in Table 20 for reactivation. The reactivated catalyst was reused in partial oxidation under the same conditions as mentioned above. The results are shown in Table 20.

As seen from Table 20, treatment with an inorganic alkaline substance or a reducing substance shows recovery of the catalytic activity.

                                      Table 20                                     __________________________________________________________________________                       Reactivated                                                  Catalyst    A.sub.20                                                                          B.sub.20                                                                          D.sub.20 -1                                                                          D.sub.20 -2                                                                          D.sub.20 -3                                                                          D.sub.20 -4                                Condi-                                                                              Reactivating                                                                          -- -- 0.375N                                                                               0.375N                                                                               1.0%  2.0%                                       tions                                                                               agent        NaOH  NaOH  Formal-                                                                              Sodium                                     of                            dehyde                                                                               formate                                    treat-                                                                         ment                                                                           for  Temper-                                                                               -- -- 30    100   60    20                                         reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              -- -- 1.0   1.0   1.0   1.0                                             (ata)                                                                          Time (hrs)                                                                            -- -- 3.0   3.0   3.0   3.0                                             Post-treat-                                                                           -- -- Water washing: 100° C.                                                              Water washing: 75° C.,                         ment            2 hrs.      3 hrs.                                                          Drying: 100° C., 16 hrs.                                                            Drying: 100° C., 16 hrs.                  Elimina-                                                                            Carbo- -- -- 12    52     0     0                                         tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             -- -- 32    95    70    55                                         materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      43 17  21   33    21    21                                          (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         58 -- --    67    170   172                                        required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________

EXAMPLE 27

The reactivated catalysts as obtained in Example 26 (Catalysts D₂₀ -1 to D₂₀ -4) were each subjected to further treatment for reactivation under the conditions as shown in Table 21. The thus reactivated catalysts were each reused for continuous partial oxidation under the same conditions as shown in Example 26. The results are shown in Table 21.

As seen from Table 21, the catalysts (E₂₁ -1 to E₂₁ -4) reactivated in two steps are much more recovered in catalytic activity than the catalysts (D₂₀ -1 to D₂₀ -4) reactivated in one step.

                                      Table 21                                     __________________________________________________________________________     Catalyst    E.sub.21 -1                                                                          E.sub.21 -2                                                                          E.sub.21 -3                                                                          E.sub.21 -4                                      Catalyst used                                                                              D.sub.20 -1                                                                          D.sub.20 -1                                                                          D.sub.20 -3                                                                          D.sub.20 -4                                      __________________________________________________________________________     Condi-                                                                              Reactivating                                                                          1.0%  0.3%  0.375N                                                                               0.375N                                           tions                                                                               agent  Hydra-                                                                               Sodium                                                                               NaOH  NaOH                                             of          zine  boro-                                                        treat-            hydride                                                      ment                                                                           for  Temper-                                                                               60    20    80    80                                               reacti-                                                                             ature (° C.)                                                       vation                                                                              Pressure                                                                              1.0   1.0   1.0   1.0                                                   (ata)                                                                          Time (hrs)                                                                            3.0   3.0   3.0   3.0                                              Post-treat- Water washing: 75° C.,                                                              Water washing: 100° C.,                         ment           3 hrs.      2 hrs.                                                          Drying: 100° C., 16 hrs.                                                            Drying: 100° C., 16 hrs.                        Elimina-                                                                            Carbo- 12    52    47    47                                               tion per-                                                                           naceous                                                                   centage                                                                             materials                                                                 of                                                                             poisonous                                                                           Sulfurous                                                                             95    97    92    93                                               materials                                                                           materials                                                                 (%)                                                                            Specific surface area                                                                      34    40    39    37                                                (m.sup.2 /g-Ru)                                                               Amount of catalyst                                                                         68    62    60    62                                               required for reac-                                                             tion (ml)                                                                      __________________________________________________________________________ 

What is claimed is:
 1. A method for reactivation of a platinum group metal catalyst which comprises contacting a platinum group metal catalyst lowered in the catalytic activity as the result of having been used for steam-reforming of hydrocarbons or alkanols with an aqueous solution of an inorganic alkaline compound of alkali metal or alkaline earth metal or mixtures thereof in a concentration of 0.001 to 10 N at a temperature of 5° to 250° C. until the catalytic activity of the catalyst is substantially recovered.
 2. The method according to claim 1, wherein the inorganic alkaline compound is a member selected from the group consisting of hydroxides, carbonates, nitrates and sulfates of sodium, potassium, calcium, magnesium, barium and strontium.
 3. The method according to claim 1, followed by treatment with at least one of hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 50 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 4. The method according to claim 1, wherein the catalyst is previously treated with at least one of hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 10 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 5. The method according to claim 1, wherein the catalyst is previously contacted with an aqueous solution of a reducing substance in a concentration of 0.01 to 10% by weight at a temperature of 5° to 250° C. for a period of 3 minutes to 80 hours and then treated with at least one of hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 50 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 6. A method for reactivation of a platinum group metal catalyst which comprises contacting a platinum group metal catalyst lowered in the catalytic activity as the result of having been used for steam-reforming of hydrocarbons or alkanols with an aqueous solution of a reducing substance in a concentration of 0.01 to 10% by weight at a temperature of 5° to 250° C. until the catalytic activity of the catalyst is substantially recovered.
 7. The method according to claim 6, wherein the reducing substance is a member selected from the group consisting of hydrazine, formaldehyde, sodium borohydride, lithium aluminum hydride, sodium tartrate, potassium tartrate, sodium potassium tartrate, calcium tartrate, sodium hydrogen tartrate, sodium formate, potassium formate, calcium formate and glucose.
 8. The method according to claim 6, followed by treatment with at least one hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 50 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 9. The method according to claim 6, wherein the catalyst is previously treated with at least one of hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 50 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 10. The method according to claim 6, wherein the catalyst is previously contacted with an aqueous solution of an inorganic alkaline compound of alkali metal or alkaline earth metal or mixtures thereof in a concentration of 0.001 to 10 N at a temperature of 5° to 250° C. for a period of 3 minutes to 80 hours and then treated with at least one of hydrogen, oxygen and steam at a temperature of 350° to 750° C. under a pressure of 1 to 50 atm. (absolute) until poisonous materials deposited on the catalyst are eliminated.
 11. A method for reactivation of a platinum group metal catalyst which comprises contacting a platinum group metal catalyst lowered in the catalytic activity as the result of having been used for steam-reforming of hydrocarbons or alkanols with an aqueous solution or a reducing substance in a concentration of 0.01 to 10% by weight at a temperature of 5° to 250° C. for a period of 3 minutes to 80 hours and then treating the catalyst with an aqueous solution of an inorganic alkaline compound of alkali metal or alkaline earth metal or mixtures thereof in a concentration of 0.001 to 10 N at a temperature of 5° to 240° C. until the catalytic activity of the catalyst is substantially recovered. 